IS-GPS-200H (797934), страница 24
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In general, any message type 30’s (i.e. 30-39) will provide SV clock correctionparameters as described in this section.164IS-GPS-200H24 Sep 201330.3.3.2.1.1 SV Clock Correction.Any one of message types 30 through 37, Figure 30-3 through Figure 30-10, contains theparameters needed by the users for apparent SV clock correction. Bits 61 to 71 contain toc , clockdata reference time of week. Bits 72 to 127 contain SV clock correction coefficients.
Therelated algorithm is given in paragraph 20.3.3.3.3.1.30.3.3.2.1.2 Data Predict Time of Week.Bits 39 through 49 of message types 30 through 37 shall contain the data predict time of week(top). The top term provides the epoch time of week of the state estimate utilized for theprediction of SV clock correction coefficients.30.3.3.2.2 Clock Parameter Characteristics.The number of bits, the scale factor of the LSB (which is the last bit received), the range, and theunits of clock correction parameters shall be as specified in Table 30-III.30.3.3.2.3 User Algorithms for SV Clock Correction Data.The algorithms defined in paragraph 20.3.3.3.3.1 allow all users to correct the code phase timereceived from the SV with respect to both SV code phase offset and relativistic effects.However, since the SV clock corrections of equations in paragraph 20.3.3.3.3.1 are estimated bythe CS using dual frequency L1 and L2 P(Y) code measurements, the single-frequency L1 or L2user and the dual-frequency L1 C/A - L2 C users must apply additional terms to the SV clockcorrection equations.
These terms are described in paragraph 30.3.3.3.1.165IS-GPS-200H24 Sep 2013Table 30-III.Clock Correction and Accuracy ParametersParameterNo. ofBits**ScaleFactor(LSB)EffectiveRange***300604,500tocClock Data Reference Time of Week11URANED0IndexNED Accuracy Index5*URANED2Indexaf2-naf1-naf0-nNED Accuracy Change Index3NED Accuracy Change Rate Index10*2-6020*2-4826*2-35SV Clock Drift Rate CorrectionCoefficientseconds(seetext)3URANED1IndexUnits(seetext)SV Clock Drift CorrectionCoefficient(seetext)sec/sec2sec/secSV Clock Bias Correction Coefficientseconds****Parameters so indicated are two’s complement, with the sign bit (+ or -) occupying the MSB;**See Figure 30-3 through 30-10 for complete bit allocation in Message types 30 to 37;Unless otherwise indicated in this column, effective range is the maximum range attainable withindicated bit allocation and scale factor.30.3.3.2.4 Non-Elevation-Dependent (NED) Accuracy Estimates.Bits 50 through 54, and 55 through 57, and 58 through 60 of message types 30 through 37 shallcontain the non-elevation-dependent (NED) component URANED0 Index,URANED1 Index, andURANED2 Index, respectively, of the SV (reference paragraph 6.2.1) for the standard positioningservice user.
The following equations together with the broadcast URANED0 Index, URANED1Index, and URANED2 Index shall give the non-elevation dependent user range accuracy ofIAURANED over the current clock/ephemeris fit interval. While the actual NED related URAmay vary over the satellite footprint, the IAURANED calculated using the parameters in messagetype 10 at each instant during the current clock/ephemeris fit interval shall bound the maximumIAURANED expected for the worst-case location within the satellite footprint at that instant.The user shall calculate the NED-related URA with the equation (in meters);IAURANED = URANED0 + URANED1 (t - top + 604,800*(WN - WNop))166IS-GPS-200H24 Sep 2013for t - top + 604,800*(WN - WNop) ≤ 93,600 secondsIAURANED = URANED0 + URANED1*(t - top + 604,800*(WN - WNop)) + URANED2*(t - top +604,800*(WN - WNop) - 93,600)2for t - top + 604,800*(WN - WNop) > 93,600 secondswheret is the GPS system timeThe CS shall derive URANED0, URANED1, and URANED2 indexes which, when used together inthe above equations, results in the minimum IAURANED that is greater than the predictedIAURANED during the clock/ephemeris fit interval.Non-elevation dependent URA (URANED) accounts for signal-in-space contributions to userrange error that include, but are not limited to, the following: the net effect of clock parameterand code phase error in the transmitted signal for single-frequency L1C/A or single-frequencyL2C users who correct the code phase as described in Section 30.3.3.3.1.1.1, as well as the neteffect of clock parameter, code phase, and intersignal correction error for dual-frequency L1/L2and L1/L5 users who correct for group delay and ionospheric effects as described in Section30.3.3.3.1.1.2.The user shall use the broadcast URANED0 index to derive the URANED0 value.
The URANED0index is a signed, two’s complement integer in the range of +15 to -16 and has the followingrelationship to the URANED0 value:167IS-GPS-200H24 Sep 2013URANED0 IndexURANED0 (meters)156144.00< URANED0 (or no accuracy prediction is available)143072.00< URANED0≤6144.00131536.00< URANED0≤3072.0012768.00< URANED0≤1536.0011384.00< URANED0≤768.0010192.00< URANED0≤384.00996.00< URANED0≤192.00848.00< URANED0≤96.00724.00< URANED0≤48.00613.65< URANED0≤24.0059.65< URANED0≤13.6546.85< URANED0≤9.6534.85< URANED0≤6.8523.40< URANED0≤4.8512.40< URANED0≤3.4001.70< URANED0≤2.40-11.20< URANED0≤1.70-20.85< URANED0≤1.20-30.60< URANED0≤0.85-40.43< URANED0≤0.60-50.30< URANED0≤0.43-60.21< URANED0≤0.30-70.15< URANED0≤0.21168IS-GPS-200H24 Sep 2013-80.11< URANED0≤0.15-90.08< URANED0≤0.11-100.06< URANED0≤0.08-110.04< URANED0≤0.06-120.03< URANED0≤0.04-130.02< URANED0≤0.03-140.01< URANED0≤0.02URANED0≤0.01-15-16No accuracy prediction available-use at own riskFor each URANED0 index (N), users may compute a nominal URANED0 value (X) as given by:• If the value of N is 6 or less, but more than -16, X = 2(1 + N/2),• If the value of N is 6 or more, but less than 15, X = 2(N - 2),• N = -16 or N = 15 shall indicate the absence of an accuracy prediction and shall advise thestandard positioning service user to use that SV at his own risk.For N = 1, 3, and 5, X should be rounded to 2.8, 5.7, and 11.3 meters, respectively.The nominal URANED0 value (X) shall be suitable for use as a conservative prediction of theRMS NED range errors for accuracy-related purposes in the pseudorange domain (e.g.,measurement de-weighting RAIM, FOM computations).
Integrity properties of the IAURANEDare specified with respect to the scaled (multiplied by either 4.42 or 5.73 as appropriate) upperbound values of the URANED0 index, URANED1 index, and URANED2 index (see 30.3.3.1.1).URANED0 accounts for zeroth order SIS contributions to user range error which include, but arenot limited to, the following: LSB representation/truncation error; the net effect of clockcorrection polynomial error and code phase error in the transmitted signal for single-frequencyL1C/A or single-frequency L2C users who correct the code phase as described in Section30.3.3.3.1.1.1; the net effect of clock parameter, code phase, and inter-signal correction error fordual-frequency L1/L2 and L1/L5 users who correct for group delay and ionospheric effects asdescribed in Section 30.3.3.3.1.1.2; radial ephemeris error; anisotropic antenna errors; and signaldeformation error.
URANED0 does not account for user range contributions due to the inaccuracy169IS-GPS-200H24 Sep 2013of the broadcast ionospheric data parameters used in the single-frequency ionospheric model orfor other atmospheric effects.The transmitted URANED1 index is an integer value in the range 0 to 7. The URANED1 index hasthe following relationship to the URANED1 value:1NURANED1 = 2 (meters/second)whereN = 14 + URANED1 IndexThe transmitted URANED2 index is an integer value in the range 0 to 7.
URANED2 index has thefollowing relationship to the URANED2:1NURANED2 = 2 (meters/second2)whereN = 28 + URANED2 Index.30.3.3.3 Message Type 30 Ionospheric and Group Delay Correction Parameters.30.3.3.3.1 Message Type 30 Ionospheric and Group Delay Correction Parameter Content.Message type 30 provides SV clock correction parameters (ref.
Section 30.3.3.2) and ionosphericand group delay correction parameters. Bits 128 through 192 of message type 30 provide thegroup delay differential correction terms for L1, L2, and L5 signal users. Bits 193 through 256provide the ionospheric correction parameters for single frequency users. The followingalgorithms shall apply when interpreting the correction parameters in the message.The broadcast group delay differential correction terms apply to the pseudorange measurementsproduced by an ideal correlation receiver with a bandwidth of 20.46 MHz centered at thereference waveform nominal frequency whose phase is linear over that bandwidth using an exactreplica of the reference waveform in an early-late discriminator having a correlator spacing of97.75 nanoseconds. The group delay differential correction terms may not apply to pseudorangemeasurements produced by different methods due to potential distortion of the transmittedwaveform.
Users employing pseudorange measurement methods different from the defined170IS-GPS-200H24 Sep 2013method must account for the potential inapplicability of the group delay differential correctionterms.30.3.3.3.1.1 Estimated L1-L2 Group Delay Differential.The group delay differential correction terms, TGD, ISCL1C/A, ISCL2C for the benefit of singlefrequency L1 P, L1 C/A, L2 P, L2 C users and dual frequency L1/L2 users are contained in bits128 through 166 of message type 30 (see Figure 30-3 for complete bit allocation). The bitlength, scale factors, ranges, and units of these parameters are given in Table 30-IV.
The bitstring of “1000000000000” shall indicate that the group delay value is not available. The relatedalgorithm is given in paragraphs 30.3.3.3.1.1.1 and 30.3.3.3.1.1.2Table 30-IV.ParameterNo. ofBits**Group Delay Differential Parameters ****Scale Factor(LSB)EffectiveRange***Units-35secondsTGD13*2ISCL1C/A13*2-35secondsISCL2C13*2-35secondsISCL5I513*2-35secondsISCL5Q513*2-35seconds*Parameters so indicated are two’s complement with the sign bit (+ or -) occupying the MSB;**See Figure 30-3 for complete bit allocation in Message type 30;***Effective range is the maximum range attainable with indicated bit allocation and scale factor;**** The bit string of “1000000000000” will indicate that the group delay value is not available.30.3.3.3.1.1.1 Inter-Signal Correction.The correction terms, TGD, ISCL1C/A and ISCL2C, are initially provided by the CS to account forthe effect of inter-signal biases between L1 P(Y) and L2 P(Y), L1 P(Y) and L1 C/A, andbetween L1 P(Y) and L2 C, respectively, based on measurements made by the SV contractorduring SV manufacture.
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